Internal combustion engines for vehicles include a plurality of cylinders. For V-type engines, the cylinders are divided into two banks of cylinders that are arranged at an angle with respect to each other. Some examples of V-type engines are V6 engines (two banks of 3 cylinders each), V8 engines (two banks of 4 cylinders each), and V10 engines (two banks of 5 cylinders each). In order to improve performance, fuel economy, and/or emissions, V-type engines could incorporate variable valve lift (VVL) systems. VVL systems enables engines to alter their peak valve lift and opening duration depending on operating conditions. In overhead camshaft V-type engines, two different intake camshafts are utilized for the two cylinder banks. Each intake camshaft actuates a separate set of rockers arms, which in turn actuate a separate set of intake valves for a respective cylinder bank.
In one implementation, a two-step VVL system utilizes specifically configured rocker arms and tri-lobe intake camshafts to provide for valve lift and opening duration to be toggled between two modes: a default or low lift mode and a high lift mode. In the low lift mode, the two outer cam lobes engage the rocker arm, which actuates the intake valves. If the high lift mode is desired, an oil pressure regulating solenoid or valve supplies oil to the rocker arm assembly, which pushes a pin under the rocker arm to allow the middle lobe of the tri-lobe camshaft to engage the rocker arm and actuate the intake valve. This VVL system allows the V-type engine to effectively have both a performance mode (the high lift mode) and an efficiency mode (the low lift mode). Low valve lift provides for fuel economy increases by reducing V-type engine pumping work, while high lift enables or provides for increased performance (e.g., increased power).
During operation of a V-type engine with this two-step VVL system in the low lift mode, there could be a greater sensitivity to any cylinder bank to cylinder bank airflow imbalance. For example, when in low lift mode, the intake valves are open for a reduced period of time with a reduced peak valve lift. As a result, if there is any difference in the opening point of the intake valves on one cylinder bank compared to the other cylinder bank, there could be a significant difference in the total amount of air inducted into each cylinder bank, and thus the torque produced by each cylinder bank. If there is a significant difference in the torque produced by each cylinder bank, then V-type engine stability could decrease, which may compromise fuel economy, performance, emissions, and/or NVH. Accordingly, there is a need for improvement in the relevant art.